Does anyone ever put those insulating blankets on their wooden doors? I have a two-car garage and want to try to keep the garage as warm as possible. (Minimum of -20°F winters). Would insulation on a wooden door invite mold, or would a garage door be drafty enough to not have to worry?

Where would these blankets be found? Are fiberglass blankets ideal, or are the foil-lined "bubble-wrap" styles better?